Various forms of seats, particularly vehicle seats used in various types of motive vehicles, incorporate seat suspensions in both the seat base (i.e. the portion that contacts the lower body of a user, including the legs) and seat back (i.e. the portion that contacts the upper body of a user, including the back, arms, neck, and head) to support the weight of a user, such as a vehicle operator or passenger. The users can have significant differences, including, for example, different weights and weight distributions, body types, shapes (e.g. male and female), and sizes (e.g. overall heights and widths, as well as leg, arm, neck, and head sizes). It is frequently desirable to provide adjustable seats, particularly seats with adjustable seat suspensions in the seat base and seat back, to accommodate these differences and provide a comfortable seat for the user.
Various approaches have been employed to provide adjustable seats, including those that provide heating and cooling elements, adjust the back support (e.g. lumbar regions), adjust the thigh support (e.g. various adjustable side and seat bolsters), and change the size of the seat. These seats have included adjustable seat suspensions that incorporate various inflatable elements, such as air bladders, as well as those that incorporate certain shape memory alloy (SMA) elements.
Notwithstanding the existence of prior adjustable seat suspensions and seats that incorporate them, different users may find seats and seat suspension systems either too firm (too hard) or not firm enough (too soft) for their liking. Therefore, there remains a need for new adjustable firmness seat suspensions and seats incorporating them that are configured to provide improved degrees or levels of firmness that better satisfy user requirements and/or that provide a lower cost.